Well-established power distribution systems exist throughout most of the United States, and other countries, that provide power to customers via power lines. With some modification, the infrastructure of the existing power distribution systems can be used to provide data communication in addition to power delivery, thereby forming a power distribution communication system. In other words, existing power lines, that already have been run to many homes and offices, can be used to carry data signals to and from the homes and offices. These data signals are communicated on and off the power lines at various points in the power distribution communication system, such as, for example, near homes, offices, Internet service providers, and the like.
While the concept may sound simple, there are many challenges to overcome in order to use power lines for data communication. Power distribution systems include numerous sections, which transmit power at different voltages. The transition from one section to another typically is accomplished with a transformer. The sections of the power line distribution system that are connected to the customers typically are low voltage (LV) sections having a voltage between 100 volts and 240 volts, depending on the system. In the United States, the low voltage section typically is about 120 volts (120V). The sections of the power distribution system that provide the power to the low voltage sections are referred to as the medium voltage (MV) sections. The voltage of the MV section is in the range of 1,000 volts to 100,000 volts. The transition from the MV section to the LV section of the power distribution system typically is accomplished with a distribution transformer, which converts the higher voltage of the MV section to the lower voltage of the LV section.
Power system transformers are one obstacle to using power distribution lines for data communication. Transformers act as a low-pass filter, passing the low frequency signals (e.g., the 50 or 60 Hz power signals) and impeding high frequency signals (e.g., frequencies typically used for data communication) from passing through the transformer. As such, power distribution communication systems face the challenge of passing the data signals around, or through, the distribution transformers.
As discussed, medium voltage power lines can operate from about 1000 V to about 100 kV, and often have high current flows. The transformer bypass devices couple data to and from the medium voltage power line—often processing the data signals with conventional signal processing circuitry that is typically powered by voltages in the range of 3.3 volts to 5 volts direct current (DC).
FIG. 1 is a schematic representation illustrating an example of a bypass system having a power line coupler 10 that couples data to and/or from the medium voltage power line. From the power line coupler 10 the data signals are coupled to a signal processor 15, an electrically non-conductive path 50a, a medium voltage modem 20, a data router 30, a low voltage modem 40, a second electrically non-conductive path 50b, a low voltage power line coupler 60, and on to a low voltage power line. Data flow from the low voltage power line to the medium voltage power line may pass through the same components in the opposite order as will be evident to those skilled in the art. This example bypass device includes two non-electrically conductive paths 50a and 50b, which permit the flow of data signals, but provide electrical isolation between the medium voltage power line and the low voltage power line. Thus, the non-electrically conductive paths 50a and 50b prevent the high voltages of the medium voltage power line from reaching the low voltage power lines and the customer premises while permitting the bi-directional communication of data signals around the transformer. Such isolation is a very important component of such systems as it ensures the safety of individuals and property, and prevents damage of equipment, using the low voltage power lines by preventing the medium voltage power from reaching the low voltage power lines.
The power line coupler 10 and/or the signal processor 15 of the bypass device may require a direct current power supply to power the electronics of these functional components. The voltage output of such a power supply typically is on the order of 3.3 volts to 5 volts DC. It would be undesirable, however, to directly connect the low voltage power line to a power supply for powering the circuitry comprising these components (the power line coupler 10 and the signal processor 15) because such a connection would not provide the necessary isolation between the low voltage and medium voltage power lines.
Prior art solutions to this problem include extracting power from the medium voltage power line and using this power to power the electronics on the medium voltage side of the electrical non-conductive paths. Some of the existing means of drawing power from the medium voltage power line include inductively or capacitively coupling power from the power line. However, the inductive method is difficult to implement due to the varying current on the medium voltage power line, which may vary from less than 1 amp to 500 amps. Similarly, capacitive coupling may require extremely large capacitors (e.g., a 10,000 volt rating) and face other technical challenges.
The power supply of the present invention provides a technique for supplying power to the medium voltage side of an isolation device, while maintaining the electrical isolation between the low voltage and medium voltage power lines. These and other advantages are provided by various embodiments of the present invention.